1. Field of the Invention
The present invention relates to a silver salt type photosensitive material used in forming an image, and to an image forming method using the photosensitive material.
More particularly, the present invention relates a photosensitive material containing a coloring matter, and an image forming method that forms an image by transferring to an image-receiving material and the like the coloring matter contained in the photosensitive material.
2. Related Background Art
Energies used to form or record an image include light, sound, electricity, magnetism, heat, radiations such as electron rays and X-rays, and chemical energy, among which, in particular, widely used are light, electricity, heat energy, or a combination of any of these.
For example, the image forming method that employs light energy and chemical energy in combination includes a silver salt photographic process and a method in which a diazo copying paper is used. The method that employs light energy and electric energy in combination includes an electrophotographic system. Also, the method that utilizes heat energy includes a method in which a thermal recording paper or transfer recording paper is used. On the other hand, known as the method that utilizes electric energy is a method in which an electrostatic recording paper, electrothermal recording paper, or electrosensitive recording paper is used.
Of the above image forming methods, the silver salt photographic process can obtain an image having a high resolution. The silver salt photographic process, however, requires the complicated developing and fixing treatments that uses liquid compositions, or the drying of an image (or a print).
Now, development is energetically made on image forming methods that can form an image through a simple processing.
For example, Japanese Patent Application Laid-Open No. 62-69062 teaches a method in which polymerization reaction under dry (thermal) conditions is caused by the photosensitive reaction of silver halide that acts as a trigger, to form an image comprising a polymer.
Japanese Patent Application Laid-Open No. 62-70836, for example, also discloses a method of forming a polymer image, comprising: forming a latent image comprising silver metal produced from silver halide by imagewise exposure; converting, under heating, a reducing agent into an oxidized product having a polymerization inhibitory power different from that of the reducing agent by utilizing a catalytic action of the above silver metal, thereby producing a difference in the polymerization inhibitory power between the reducing agent and the resulting oxidized product; and also causing a thermal polymerization reaction utilizing the thermal polymerization initiator, thus forming a polymer latent image corresponding with the difference in the polymerization inhibitory power.
From such a polymer latent image comprising polymerized areas and unpolymerized areas, an image comprising a polymer can be obtained by selectively carrying out adhesion transfer or etching of the polymerized areas or unpolymerized areas.
These methods, however, have been involved in a disadvantage that a good contrast tends not to be achieved in the polymer latent image.
This disadvantage arises presumably because the oxidation-reduction reaction taking place in a latent image portion to form the oxidized product and the polymerization reaction to form the polymer image are allowed to take place in the same heating step, so that these reactions may proceed in a competitive fashion and thus the respective reactions may not proceed in a good efficiency.
Also, the image formation according to this method is very unstable in that, for example, an areas where the polymer is formed may turn into imagewise exposed areas or unexposed areas only because of a slight change in the amount of the reducing agent to be added.
In addition, Japanese Patent Application Laid-Open No. 61-75342 discloses a method in which a reducing agent having a polymerization inhibitory power is brought into an oxidized product by imagewise consumption (at imagewise exposed areas) in the course of the developing of silver halide, and after imagewise inhibition (at imagewise unexposed areas) of polymerization reaction by the action of the residual reducing agent, light energy is uniformly applied from the outside (whole areal exposure) to cause photopolymerization at the part where the reducing agent has been consumed, thus forming a polymer image.
The above method has advantages that it can achieve a high sensitivity in the writing of a latent image since the silver halide is used, and the steps of from the writing for the formation of an image up to the whole areal exposure can be separated in a good efficiency. It, however, is difficult to obtain a polymer latent image having a sufficient contrast. This is caused by the following reason.
The reducing agent used in the above method is in itself a reducing agent that acts as a polymerization inhibitor and turns not to act as the polymerization inhibitor after the reduction of silver halide. If the polymerization is sufficiently achieved, the reducing agent at the imagewise exposed area will not be sufficiently converted into the oxidized product. However, the application of heat energy in a sufficient amount in carrying out a development, with the intention to sufficiently convert the reducing agent at the imagewise exposed area into the oxidized product, may cause an undesired oxidation-reduction reaction at the imagewise unexposed areas. To the contrary, the application of heat energy in a reduced amount in carrying out the development, with the intention to prevent the oxidation-reduction reaction from taking place at the imagewise unexposed area, may cause the oxidation-reduction reaction not to sufficiently proceed at the exposed areas. Since in this instance the imagewise exposed area of an oxidation-reduction image is polymerized with difficulty, light energy in carrying out the whole areal exposure must be applied in an increased amount. This may cause an undesired polymerization at the unexposed areas with increase in the amount of light energy, eventually making it impossible to obtain a polymer latent image with a sufficient contrast.